Strain sensing is used in a Health Monitoring System (HMS) for civilian, mechanical, and aerospace applications. The choice of sensor types for a given sensing application may depend upon a parameter being measured and the physical properties of the sensor. The parameter being measured can be strain, temperature, pressure, or force on a structure.
Common fiber optic sensors may be based on interferometric, attenuation, and spectral effects. Two major categories of fiber optic strain sensors are the Fabry-Perot interferometric and Bragg grating sensors. The irradiance output changes with strain for Fabry-Perot sensors and the wavelength output changes with strain for Bragg grating sensors. The relationship between the irradiance output and applied strain may be highly non-linear for Fabry-Perot sensors, where as the spectral shift may be linear for Bragg grating sensors. This linear property may make Bragg gratings desired sensors in strain sensing applications.